1. Field of the Invention
The invention relates in general to a method for forming a metal pad on a semiconductor Pre-Metal Dielectric (PMD) and metal pad structure using the same, and more particularly to a method for forming a metal pad on a semiconductor Pre-Metal Dielectric (PMD) which combines tungsten (W) chemical mechanic polishing (CMP) and etching back for thickness reduction of top metal and metal pad structure using the same.
2. Description of the Related Art
FIGS. 1A and 1B are schematic diagrams of the conventional top metal formation for a metal pad. As shown in FIG. 1A, after the formation of first metals 102 on a semiconductor Pre-Metal Dielectric (PMD) 100, a dielectric layer 110 is deposited to cover the first metals 102 and the semiconductor Pre-Metal Dielectric (PMD) 100 and vias 112 are formed in the dielectric layer 110. Then, a metal layer 120 is deposited to cover the vias 112 and the dielectric layer 110. Afterward, as shown in FIG. 1B, a lithography operation is performed on the metal layer 120 to form a few second metals (top metals) 130 covering the vias 112 and separated from each other.
Owing that these second metals 130 are used for a metal pad in a wafer acceptance test and package of the semiconductor Pre-Metal Dielectric (PMD) 100, normally, the second metals 130 have to be thick enough, such as 6 KA, such that the probe card would not penetrate the second metals 130 in the wafer acceptance test.
However, due to the thickness limitation of the second metals 130, after a passivation layer 140 is formed, a lot of passivation cracks 142 are often formed between the second metals 130 as shown in FIG. 1C.
Besides, due to the large thickness of the second metals 130, after the fill-in process of the passivation layer 140, the second metals 130 in an array-like pattern are usually collapsed (stress induce) as shown in FIG. 1D. As a result, a metal bridge issue (due to collapse) occurs between the second metals 130 to reduce the electric isolation effect.
As mentioned above, due to the passivation crack issue and the metal bridge issue, the reliability in electrical test of the semiconductor Pre-Metal Dielectric (PMD) 100 through the metal pad (second metals 130) is largely reduced.